Selective laser sintering (“SLS”) is a process whereby a three-dimensional article is constructed in a layer-by-layer process from powdered material. A given cross-section is formed by irradiating selected portions of a powder layer with a laser beam to melt the powder falling within a predetermined boundary of the desired cross-section. Successive layers of powder are applied and irradiated until the desired three-dimensional article has been produced. The non-irradiated powder supports the article as it is produced, allowing for overhangs and undercuts without the use of other supports. A detailed description of SLS technology can be found in U.S. Pat. Nos. 4,247,508, 4,863,538, 5,017,753, and 6,110,411, each incorporated herein by reference.
SLS technology has enabled the direct manufacture of three-dimensional articles of high resolution and dimensional accuracy from a variety of powdered materials including conventional polymer powders. These conventional powders are well suited to rapid prototyping and various other applications. However, articles produced from conventional polymer powders via SLS processes typically exhibit inferior mechanical properties relative to articles produced by more conventional manufacturing processes such as, for example, injection molding.
A further disadvantage typically associated with conventional SLS polymers is the high amount of waste that can result from their use in SLS processes. Given the selectivity of SLS processes, a substantial amount of non-irradiated powder typically remains after the production of SLS articles. Efforts have been made to reuse the non-irradiated powder for production of subsequent SLS articles. Conventional laser-sinterable polyamide powders, however, have a tendency to undergo changes (possibly caused by post-condensation reactions under the elevated temperature conditions prevailing in the forming chamber of the SLS machine), which can cause unsuitable rises in viscosity that (a) limit the further use (i.e., the “recyclability”) of the powder in subsequent SLS processes or (b) cause conventional polyamide powders to be mixed with a substantial portion of new powder before being reused. This ultimately results in the accumulation of an excess of powder that is no longer suitable for use in SLS processes.
Thus, there is a continuing need for improved powder compositions for use in producing sintered articles.